In the present study, the macroscopic sorption behaviors and microscopic immobilization mechanisms of Ni(II) at cryptomelane/water interfaces were explored using the combination of batch sorption technique, desorption procedure, theoretical simulation, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) analyses. The good simulation of the pseudo-second-order model on the sorption kinetics data suggests a driving force of chemical sorption rather than mass transport or physical interaction. The sorption trends and uptake mechanisms are obviously related to the solution pH, with cation exchange or outer-sphere surface complexation at an acidic pH of 4.0, inner-sphere surface complexation in both the edge-shared (ES) and double corner-shared (DCS) modes at a neutral pH of 7.0, and precipitation of α-Ni(OH)2(s) phase at a highly alkaline pH of 10.0. The gradual increase of Ni(II) sorption amount with solution temperature rising from 293 K to 333 K is consistent with the increased ratio of the weak DCS configuration. The research findings herein can help us better understand the migration and transformation trends of Ni(II) in the manganese mineral-riched aquatic environment.
Keywords: Cryptomelane; Immobilization mechanisms; Ni(II); Spectroscopic analyses; Theoretical simulation.
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